Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$188.70	12.254%	$211.8233	$211.82	$211.80	$211.80
Purchase #2	$150.91	11.234%	$167.8632	$167.86	$167.85	$167.90
Purchase #3	$135.75	9.504%	$148.6517	$148.65	$148.65	$148.70
Purchase #4	$148.29	12.227%	$166.4214	$166.42	$166.40	$166.40
Purchase #5	$6.72	8.194%	$7.2706	$7.27	$7.25	$7.30
Purchase #6	$94.31	10.364%	$104.0843	$104.08	$104.10	$104.10
Purchase #7	$174.96	6.276%	$185.9405	$185.94	$185.95	$185.90
7 purchase totals =	$899.64		$992.0550	$992.04	$992.00	$992.10